1. Field of the Invention
The present invention relates to an apparatus and method for testing a personal system/2 (PS/2) interface in computer interface testing.
2. General Background
PS/2 interface is a type of port developed by IBM for connecting a mouse or keyboard to a personal computer (PC). The PS/2 port supports a mini din plug containing just 6 pins. Most PCs have a PS/2 port so that the serial port can be used by another device, such as a modem.
The PS/2 interface uses a bidirectional serial protocol to transmit movement and button-position data to a computer's auxiliary device controller (keyboard controller). The computer, in turn, may send a number of commands to the mouse to set the report rate, resolution, reset the mouse, disable the mouse, etc. The computer also provides the mouse with an overload-protected 5V power supply.
The 6 pins mini-din (PS/2 style) at the computer are defined as follows:
PinNameDescription1DATAKey Data2n/cNot connected3GNDGround4VCCPower, +5 VDC5CLKClock6n/cNot connectedWhen testing the functions of the PS/2 interface of a computer, the data and clock pins of the PS/2 interface are tested.
Data transmissions to and from the auxiliary device connector consist of an 11-bit data stream sent serially over the ‘data’ line. The following table shows the function of each bit. The parity bit is either 1 or 0, and the 8 data bits (Data bit 0 to Data bit 7 as shown in the table), plus the parity bit, always have an odd number of 1's.
BITFUNCTION11Stop bit (always 1)10Parity Bit (odd partly)9Data Bit 7 (most-significant)8Data Bit 67Data Bit 56Data Bit 45Data Bit 3 (most-significant)4Data Bit 23Data Bit 12Data Bit 0 (least-significant)1Start Bit (always 0)The PS/2 mouse and keyboard implement a bidirectional synchronous serial protocol. The bus is “idle” when both lines are high. This is the only state where the keyboard/mouse is allowed begin transmitting data. The host has ultimate control over the bus and may inhibit communication at any time by pulling or keeping the clock pin to transmit at a low voltage level. The device always generates the clock signal. If the host wants to send data, it must first inhibit communication from the device by pulling clock low. The host then pulls data low and releases clock. This is the “Request-to-Send” state and signals the device to start generating clock pulses.
Typically, the PS/2 interface is installed in a host and a keyboard and/or mouse are manually operated to test functions of the interface. However, the above-mentioned testing method requires a lot of space for the keyboard and mouse and is labor intensive.
What is needed therefore, is an apparatus that can automatically test the PS/2 interface.